Interest in the percutaneous or transdermal delivery of peptides and proteins to the human body continues to grow with the increasing number of medically useful peptides and proteins becoming available in large quantities and pure form. The transdermal delivery of peptides and proteins still faces significant problems. In many instances, the rate of delivery or flux of polypeptides through the skin is insufficient to produce a desired therapeutic effect due to their large size and molecular weight. In addition, polypeptides and proteins are easily degraded during and after penetration into the skin, prior to reaching target cells. Likewise, the passive transdermal flux of many low molecular weight compounds is too limited to be therapeutically effective.
One method of increasing the transdermal delivery of agents relies on pre-treating the skin with, or co-delivering with the beneficial agent, a skin permeation enhancer. A permeation enhancer substance, when applied to a body surface through which the agent is delivered, enhances the transdermal flux of the agent such as by increasing the permselectivity and/or permeability of the body surface, and/or reducing the degradation of the agent.
Another method of increasing the agent flux involves the application of an electric current across the body surface referred to as “electrotransport.” “Electrotransport” refers generally to the passage of a beneficial agent, e.g., a drug or drug precursor, through a body surface, such as skin, mucous membranes, nails, and the like. The transport of the agent is induced or enhanced by the application of an electrical potential, which results in the application of electric current, which delivers or enhances delivery of the agent. Electrotransport delivery generally increases agent delivery and reduces polypeptide degradation during transdermal delivery.
There also have been many attempts to mechanically penetrate or disrupt the skin in order to enhance the transdermal flux. See for example, U.S. Pat. No. 5,879,326 issue to Godshall, et al., U.S. Pat. No. 3,814,097 issued to Ganderton, et al., U.S. Pat. No. 5,279,544 issued to Gross, et al., U.S. Pat. No. 5,250,023 issued to Lee, et al., U.S. Pat. No. 3,964,482 issued to Gerstel, et al., Reissue 25,637 issued to Kravitz, et al., and PCT Publication Nos. WO 96/37155, WO 96/37256, WO 96/17648, WO 97/03718, WO 98/11937, WO 98/00193, WO 97/48440, WO 97/48441, WO 97/48442, WO 98/00193, WO 99/64580, WO 98/28037, WO 98/29298, and WO 98/29365. These devices use piercing elements of various shapes and sizes to pierce the outermost layer (i.e., the stratum corneum) of the skin. The penetrating elements disclosed in these references generally extend perpendicularly from a thin, flat member, such as a pad or sheet. The penetrating elements in some of these devices are extremely small, some having dimensions (i.e., a microblade length and width) of only about 25-400 μm and a microblade thickness of only about 5-50 μm. Other penetrating elements are hollow needles having diameters of about 10 μm or less and lengths of about 50-100 μm. These tiny stratum corneum piercing/cutting elements are meant to make correspondingly small microslits/microcuts in the stratum corneum for enhanced transdermal agent delivery therethrough. In many instances, the microslits/microcuts in the stratum corneum have a length of less than 150 μm and a width which is substantially smaller than their length.
Skin penetrating devices are used to penetrate the outermost layer of the skin, i.e., stratum corneum, with a plurality of microprotrusions to form pathways through which an agent such as a drug can be introduced, i.e., delivered, or an agent such as a body analyte can be withdrawn, i.e., sampled. The perforated skin provides improved flux for sustained agent delivery or sampling through the skin.
When microprotrusion arrays are used to improve delivery or sampling of agents through the skin, consistent, complete, and repeatable penetration is desired. Manual application of a skin patch having microprotrusions protruding from its skin-contacting side often results in significant variation in puncture depth across the length and width of the patch. In addition, manual application results in large variations in puncture depth between applications due to the manner in which the user applies the array. Accordingly, it would be desirable to be able to apply a microprotrusion array to the stratum corneum with an automatic device, which provides in a consistent and repeatable manner, stratum corneum piercing not only over the length and width of the microprotrusion array but also from application of one microprotrusion array to the next.
Some known spring loaded applicator devices for delivery of lancets for body fluid (e.g., blood) sampling are described in WO 99/26539 and WO 97/42886. However, these devices are difficult to use because they require two handed cocking of the applicator device prior to application. In particular, the known spring loaded lancet applicators require either two sections of the device to be pulled apart for cocking or require one part of the device to be twisted with respect to another part of the device for cocking. In both of these motions two handed cocking operation is required. Many of the patients using these devices possess neither the strength nor the manual dexterity to cock these known applicator devices.
Accordingly, it would be desirable to provide a spring loaded applicator for a skin penetrating member which is cocked by one handed operation of the user and which requires a minimal hand strength for cocking.